Buffered stop bath for interrupted photographic development



United States Patent C) 3,284,199 BUFFERED STOP BATH FOR INTERRUPTED PHOTOGRAPHIC DEVELOPMENT Vere Maltet, East Brunswick, N.J., and Earl Delzon Peters, Staten Island, N.Y., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed May 2, 1963, Ser. No. 277,477 8 (Ilaims. (Cl. 96-50) This invention relates to photography. Particularly it relates to a process of photographic development.

The need for an effective non-ha-rmful means for temporarily halting the development of a photographic film has long been recognized in the trade, especially in the graphic arts field, where visual inspection of a film e.g., lithographic film, during development is an integral and critical part of development.

In practice, proper development of an ortho litho film which has been exposed imagewise to a continuous tone subject or through a halftone screen is accomplished by selection of an area of the negative to have a predetermined density or percent dot value. A certain percent dot (say 10%), means in the trade that 10% of the available space in the area selected for examination must be taken up by halftone dots. The density or percentage value of dots on a negative when processing has been completed can be determined by instrumental methods, but during development these values are estimated visually by inspection of a selected area, frequently with a magnifying glass in the case of halftone dots. A technician performing such development depends upon his judgment to provide a properly developed film. There are two points of concern to the technician, the first being to properly judge the density or percent dot in the area selected and the second to be able to judge rate of development.

The rate of development of lithographic films is characterized by an induction period of about 15 to 30 seconds during which time very little appears to be happening. After this point, development occurs rapidly and will be attained in times varying between about 1 /2 to 3 minutes depending upon the particular film being developed.

The need and demand for a high quality, properly developed film in the graphic arts trade does not leave even the skilled technician much latitude in development time. Most graphic arts shows require the development of their lithographic films to be stopped within :5 seconds of the optimum time and many shops have tighter limits such as :2 seconds. In such a situation, improper development time causes a loss of film and a waste of manpower. Such losses in many instances result in an average of 30 sheets of film out of every 100 not producing a satisfactory negative.

A similar problem also arises in the development of aerial cine films. The times for proper development of cine aerial films may vary between 5 and 15 minutes but the time latitude allowable to obtain a high quality negative is small. The criticality in this field of work is many times heightened, because only one exposure of the scene taken is available which makes necessary the correct development the first time.

Because of the importance of correct development in aerial photography, a solution for temporarily halting development was sought. One such solution having a pH of approximately 3 and containing a high bromide ion concentration stops development but has a number of disadvantages. First, it does not completely stop development so that, during inspection of the film, a slight amount of development occurs which is commonly called density creep. Second, continua-tion of development by reinsertion of the sheet in the developer is uneven and irregular. Third, exhaustion of the developer occurs much more rapidly, requiring the use of much larger volumes of developer. The use of such a solution is costly and generally impractical.

It is, therefore, an object of this invention to provide a process of development which allows the alternate halting and continuation of development of a photographic film without deleterious effects on the film or developer. A further object of this invention is to provide a process which instantaneously and evenly stops development. A still further object is to provide a process which allows even and instantaneous continuation of development following interruptions. A still further object is to provide a process which halts development and allows inspection of a film without so-called density creep occurring. Still further objects will be apparent from the following description of the invention. I

The foregoing objects are accomplished by the process of this invention which temporarily halts the development of a photographic film, and which permits continuation of development without deleterious effects to the film or developer. The process comprises (1) Placing an exposed photographic film containing latent silver halide images which has been partially developed, in an aqueous solution containing at least one buffering compound, said butter solution (a) Having a pH below that at which the developer becomes inactive,

(b) Having a buffering capacity such that the introduc tion of 0.10 equivalent of sodium hydroxide into 1000 milliliters of the unused buffer solution at a pH of 72:02 will cause a pH rise of not more than 5.0 pH units or less than 0.5 pH unit, and

(2) Reinserting the fil-m in the developer to continue development of the film.

In practicing the above process, development of an exposed photographic film is commenced in the usual manner using the normal silver halide developer for the particular film, care being taken not to overdevelop the film. The film is removed from the developer and placed in a buffer solution having the specified characteristics. The film is agitated in the buffer solution (usually at the same temperature as the developer) for 15-20 seconds allowing time for neutralization. It is then removed for safelight inspection. The degree of development is noted by inspection of the density or halftone dot value attained and the film is placed back in the developer for further development if desire-d. This cycle of halting and commencing development is continued until the desired density or halftone dot value is attained, after which the subsequent steps of fixation, etc., are carried out in the usual way.

The maximum pH specified for the buffer solution will of course depend on the pH at which the developer being used becomes inactive. The required pH limit may be selected from the inactive pH of the developers listed below:

(1) A typical general purpose developer for films, papers and plates has a working pH of approximately 9.8 and is inactive at pH=9.0 or below. Such a developer may be used for blue sensitive, orthochromatic and panchromatic sensitized silver halide films.

(2) A typical fast-acting, continuous tone developer has a working pH of approximately 9.3 and is inactive at pH= 8.-6 or below. Such a developer may be used for blue sensitive, orthochromatic and panchromatic sensitized silver halide films.

(3) A typical fine grain, continuous tone developer has a working pH of approximately 8.75 and is inactive at pH=8.2 or below. Such a developer may be used for blue sensitive, orthochromatic and panchromatic sensitized silver halide films.

(4) A typical developer for lithographic films has a Working pH of approximately 9:85 and is inactive at pH=9.00 or below. Such a developer is typically used for blue-sensitive and orthochromatic sensitized silver halide films.

A typical metol hydroquinone developer for X-ray films has a working pH of approximately 10.75 and is inactive at pH=9.5 or below. Such a developer is typically used for products having no sensitizing dyes present.

Developers useful with the buffers described above and shown in subsequent examples will include those types V2. The developed densities recorded were selected 10 as resulting from exposure at a specific step falling near used 1n the photograph1c field for development of blackthe middle f the density range {or each Set f tests. and-white and color films, papers and plates. The in- E l 1 active pH of other developers not covered by the above xamp 6 list can be determined experimentally or found in the Six equal film strips cut from a sheet of lithographic literature. film having a coating weight of 50 mg. of silver/dec.

The pH characteristics of the buffers of this invention (viz., a silver bromochloride emulsion containing mole are important to the extent that they must be below the percent silver bromide and 80 mole percent silver inactive pH of the developers with which they are used, chloride) were exposed simultaneously by a loott but the buffering capacity of each is still more important incandescent lamp under a 50-volt potential at a distance since it is well known that acid stop baths have a low 20 of 72 in he from th samples.

PH but are inoperable in the PTOCGSS Of this invention. The film samples were put into a general purpose metol The buffering capacity of the butters must be (1) high hydroquinone developer at the same time, with subenough to readily overcome the buffered pH Of the desequent treatment as out-lined in Table 1. veloper in a sheet of film and bring it below the inactive pH of the developer when placed in the buffer solution 5 Formula of develop used G rams and (2) low enough to be readily overcome by the alkalinity of the developer when development is reinitiated. g f 'g 'a lg'g g If the buffering capacity of the butter is too loW, it Will H dro uinone y be exhausted too rapidly and not allow a practicable q 0 mm carbonate (anhydrous) 22.5 number of sheets to be processed. On the other hand, Potassium bromide 0.6 1f the buffering capacity is too high, 1t Wlll exhaust the Water to make 1000 m1 developer more rapidly than would normally occur.

Thus to determine Whether a buffer is useful in the Formula f uff r us d: process of hi i i H (1) 6.80 g. of potassium dihydrogen phosphate dis- (1) Select any buffer combination. Solved n 900 1 1 8. of Water.

(2) Add sufficient amounts of the buffer constituents sodium hYdT'OXidB 1s addfid until the P is i in a one liter beaker staying within the limits of solubility of the substituents. In doing so, bring the pH of a 1 liter Water addfid make a t al V lum of 1000 l ti t H 7,212, ml. Under the method of this invention the above buffer (3) Add 0.1 equivalent of sodium hydroxide (NaOH) 40 has a ibuffinng p y 'coTfeSpoIlding to P ehange to the 1 liter solution. A one liter solution (prepared of P unitsi Solution has a throughput p y as in 2 hi h increases i PH b no less than 5 pH of 1500 to 1750 sq. inches of film per liter using the film it nd no more h 5 H units h treated as d described above flashed and developed for 2 /2 minutes scribed is suitable for the process of this invention. The in t e c mp sition Shown.

TABLE I.USE OF BUFFER SOLUTION Film First Butler Safe- Second Fixed, Sample Devol- Solution, light Dovcl- Washed Developed Number opulent 20 8005. Table, opment; and Density (Mins.) 30 Secs. (Mins) Dried 1 I! an ordinary acid stop bath (approx. 1.3% acetic acid in water by volume) is substituted for the Butter Solution, return of the film to the developer as in Stop 6 above results in direct degradation of the developer by reduction of pH. Moreover, roinitiation of development occurs in a sporadic and uneven manner, giving uneven densities of unpredictable magnitude. lower pH change limit of 0.5 pH units represent a buffer of high buifering capacity. It was found that a buffer having a smaller pH change than 0.5 pH unit would start to increase the exhaustion rate of the developer, but higher pH change-s show no harmful effects to the developer.

The higher pH change limit of 5.0 represents a buffer of lower buifering capacity. Such a limit is a practical one and a buffer possessing such a buffering capacity can pass a minimum of 400 sq. inches/liter of film which has first been passed through a developer. A preferred range of pH increase for a liter of buffer solution at a pH: 72:02 is no less than 0.5 pH unit and no more than 2.0 pH uni-ts.

Points of particular interest illustrated by these data are noted as follows:

(a) Comparison of Samples 1 and 3 shows that immersion of the film in the buffer solution halts develop ment instantly.

(b) Comparison of Samples 1 and 4 shows that use of the buffer solution allows inspection of the fihn on a safelight table without attendant density increase.

(c) Comparison of Samples 1 and 5 illustrates the magnitude of density increase during inspection to be expected if the buffer solution treatment is not employed.

((1) Samples 1 and 2 show the density difference between 2 and 2 /2 minutes development.

(e) The equivalence of densities of Samples 2 and 6 shows the absence of a second induction period during the second development, and also shows that the end re- (a) Dots on Samples 1, 3 and 4 were not detectably sult is determined by the total development time and is different from each other.

not influenced by the fact that there was an interruption (b) Dots on Samples 2 and 6 were not detectably during the development. diiferent from each other but were, as expected, larger The foregoing discussion and description of the use of 5 than the dots on Samples 1, 3 and 4.

buffer solutions in controlling development has involved (c) The dots on Sample 5 were definitely larger and line exposures and a developer designed for that type eX- filled in relative to those on Samples 1, 3 and 4.

posure. Another area of great interest involving the use (d) The observation noted in (a) shows that treatment of lithographic films is that of halftone exposures with in the buffer solution halts growth of the halftone dots subsequent development in a high contrast litho developer 10 and allows inspection of the film on a safelight table withof the hydroquinone-paraforrnaldehyde type or similar out attendant dot growth. developers. While it iS much more difficult 0 present (e) The result recorded in (b) shows the absence of quantitative data describing the formation and charactera second induction period during the second developistics of halftime (1053, as was done in Table I r l ment, and also shows that the end result is determined by exposure density relationships, it may be tat t the the total development time and is not influenced by the action and efiectiveness of the bufier solution in controlf th t th was an i t ti d i th d l ling the formation of halftone dots is the same as that deme t, scribed and illustrated for line exposures. The following (f) Th d t growth i di t d i during i tio qualitative description Will SCIVC t0 illustrate the point. ithout prior treatment in the buffer solution is a manifestation of uncontrolled and undesirable continuation of Example II development during the inspection period.

Example III Six equal film strips cut from the lithographic film of Six equal fihn strips cut from a sheet of X-ray film (21 Example I and a different lithographic film having a silver iodobromide emulsion containing, 1.7% silver iodide bromochloride emulsion containing 30 mole percent silver 25 and 98.3% silver bromide and a coating weight of 120 bromide and 70 mole percent silver chloride and a coating mg. of silver/dec?) were exposed simultaneously by a weight of 51.5 mg. of silver/dec. were exposed simul- 100-watt lamp under a 25-volt potential at a distance of taneously in a manner analogous to Example I using a 72 inches from the samples. l00-watt incandescent lamp under 85-volt potential 72 The film samples were put simultaneously into a typical inches from the samples. The samples of each type were X-ray developer with subsequent treatment as outlined in exposed in contact with a magenta screen (150 lines/inch) Table III. to produce approximately a 50% dot when developed 2 /2 Formula of developer used: minutes at 68 F. in a typical high contrast lithographic Grams developer. The film samples were put into the developer Me ol 5 simultaneously, with subsequent treatment as outlined in S diu Sulfite n y r Table 1 Hydroquinone 75 Formula f developer used; Sodium carbonate (anhydrous) 50.0 Grams Potassium bromide 4-5 Metol 5 Water to make 1000 ml. Sodium sulfite 22-5 Formula of buffer used: Hydroquinone 6.0 (1) 80.0 gr. of boric acid crystals dissolved in 900 Sodium carbonate (anhydrous) 3'40 mls. of Water. Potassium bromide 1.0 (2) Sodium hydroxide is added until the pH=7.2 0i20.

Water to make 1000 ml. (3) Water is added to make a total volume of 1000 ml.

The above formula has a buifering capacity correspond- The buffer used was the same as described in Examing to a H change of 1.5 pH units when tested by the Ple I. method of this invention.

TABLE IIL-USE OF BUFFER SOLUTION First Safc- Second Fixed, Film Devel- Buffer light Devel- Washed Developed Sample oprnent Solution, Table, opment and Density Number Time 20 Secs. Secs. Time Dried (Mins) (Mins.)

TABLE OF BUFFER SOLUTION The results here parallel those described in points (a) through (e) in Example I. Further, this example il- ILlft ure l 1 one expos lustrates the use of a second bufi'er wlthan the designated T S 1 girstl sBluger s e e 0n d gix d range specified by the invention besides demonstrating the *lm am eve o u ion, ig l eve as e I Niunber e opment 20 Secs. Table, opment and workab'lhty of the Process on Y films- (Mins) 30 Secs. (Mina) Dried Example IV 2 No 0 Yes 2% N0 0 Yes.

2 $3 8 Six equal film strips from a paper product (a silver 3 iodo-chlorobromide emulsion containing 3.6 mole per cent silver iodide, 16.4 mole percent silver chloride and Based on inspection of the halftone dots at magnification H1013 P Silver bromide havlng g 10 and x, the following observations and conclu- 75 weight of 22.4 mg. of silver/dec?) for making prints of sions apply to each film type: film negatives were exposed simultaneously through a step wedge by a 100-watt lamp under a SO-volt potential at a distance of 72 inches from the samples.

The film samples were simultaneously put into a general purpose metol hydroquinone developer as described in Example I with subsequent treatment as outlined in Table (9) Strip No. 9 was removed from the buffer solution after 1 hours and fixed and washed.

Strip No. 10 was removed from the butter solution after 2 hours and fixed and washed.

(11) Strip No. 11 was removed from the buffer solu- IV. 5 tion after 4 hours and fixed and washed.

The butter use-d was the same as that described in Results.Densities were equal on all the test strips. Example III. Conclusion-There is no practical limitation on how TABLE IV.USE 0F BUFFER SOLUTION Film First Buffer Safe- Second Fixed, Sample Devel- Solution, light Devel- Washed Developed Number opment Sees. Table, opment and Density 1 (Mins.) 60 Secs. (Mins) Dried 1 0 Yes 1. 09 1 0 1 1.10 1 0 1.08 2 0 1. 69 1 1 1. 70 1 1 1. s7

1 At a specific step of the wedge exposure.

The above results parallel those described in points (a) through (e) in Example I and demonstrate the workability of the process on a paper product.

Example V Test.-A high contrast parafor-maldehyde-hydro quinone type developer was prepared and 1,000 milliliter portions were placed in each of two trays. Exposed sheets of lithographic film of the type described in Example I were successively developed in each developer and handled as specified.

(1) The sheets from develop-er N0. 1 were immediately fixed and washed in the usual fashion.

(2) Each sheet from developer No. 2 was immersed in the buffer solution for seconds, with agitation, and then returned to the developer. The two development periods in developer No. 2 were made equal in total time to the single development time period in developer No. 1. Following the second development period, the sheets were fixed and washed.

Results.Measu-red as the rate of fall in density of the processed film as the test proceeded, the exhaustion rates of the two developers were identical, within the limits of reproducibility, to the exhaustion rates of two developers without the use of an intervening bufier solution.

C0nclusion.Return of a film to the developer after treatment in the buffer solution has no deleteriou effect on the developer. The above example used the buffer described in Example III.

Example VI T est.A sheet of lithographic film of the type described in Example I was exposed through a step wedge and then cut into strips which were developed in a high contrast paratformaldehyde-hydroquinone type developer and then treated as follows.

(1) Strip No. 1 was immediately fixed and washed in the usual fashion.

Strips 2 through 11 were immersed in the bufier solution (butter solution described in Example III) and then handled as specified.

Strips 2 through 6 were removed irom the buffer solution after 30 seconds and hung in air in darkness. Strips 7 through 11 were left in the buffer solution.

(2) Strip No. 2 was fixed and washed after 5 minutes.

(3) Strip No. 3 was fixed and washed after 30 minutes.

(4) Strip No. 4 wa fixed and washed after 1 hour.

(5 Strip No. 5 was fixed and washed after 2 hours.

(6) Strip No. 6 was fixed and washed after 4 hours.

(7) Strip No. 7 was removed from the buffer solution after 1 hour and fixed and washed.

(8) Strip No. 8 was removed from the buffer solution after 30 minutes and fiXt d and Washed.

long films may he left in the buffer solution, nor on how long development of the film is interrupted after removal from the butter solution. It is noteworthy that film samples 3 through 6 were dry before the end of the period of exposure to air.

Suitable emulsions for operation with the process of this invention are silver chlorobromide, silver iodobromide andsilver iodochlorobromide. In addition to mixed silver halides, the silver halides used may be pure silver halides erg. silver bromide, silver chloride.

In place of gelatin, other natural or synthetic waterpermeable, organic colloid, binding agents can be used. Such agents include water permeable or water soluble polyvinyl alcohol and its derivatives, e.g., partially hydrolyzed polyvinyl acetates, polyvinyl ethers, and acetals containing a large number of extralinear CH CHOH groups: hydrolyzed interpoly mers of vinyl acetate and unsaturated addition polymerizable compounds such as maleic anhydr-ide, acrylic and methacrylic acid ethyl esters, and styrene. Suitable colloids of the last mentioned type are disclosed in US. Patents 2,276,322, 2,276,323, and 2,397,866. The useful polyvinyl acetals include polyvinyl acetaldehyde acetal, polyvinyl butyradehyde acetal and polyvinyl sodium o-sulfobenzaldchyde acetal. Other useful colloid hind-ing agents include the poly-N-vinyllactams of Bolton US. Patent 2,495,918, the hydrophilic copolymers of N-acrylamido alkyl betaines described in Shacklett US. Patent 2,833,650, and hydrophilic cellulose ether and esters.

The emulsions can contain known antifo ggants, e.g., 6-nitrobenzimidazole, bcnzotri-azole, triazaindenes, etc., as well as the usual hardeners, i.e., chrome alum, formaldehyde, dimethylol urea, mucochloric acid, etc. Other emulsion adjuv ants that may be added comprise sensitizers, matting agents, plasticizers, toners, optical brightening agents, etc.

The emulsions may be coated on any suitable sup port, e.g., cellulose esters, cellulose mixed esters; superpolymers, e.g., polyvinyl chloride covinyl acetate; polyvinyl acetals, e.g., tormals, acetals, butyrals; polystyrene, polyamide, e.g., polyhexamethylene adipamide; polyesters, e.g., polycarbonates, polyethylene terephthalates, polyethylene terephthalate/isophthalate, esters formed by condensing terephthalic acid and dimethyl terephthalate with propylene glycol, diethylene glycol, tetramet-hylene glycol or cyclohexane-l,4 dimethanol(hexahydrop-xylene alcohol); paper and glass.

Suitable developers for the process of this invention are the alkaline developers which include polyphenolic developers e.g., hydroquinone, pyrogallol, pyr-ocatechol, 2,3-dichlorohydroquinone; aminophenols e.g., .paminophenol, metol, 2,4-diaminophenol; polyamines e.g., pphenylenediamine, p diethylaminoaniline, n B methyl sulfonamidoethyl-4-aminoaniline; heterocyclic bases e.g.,

pdihydroxyquinoline, amino and hydroxymorpholines, 1- phenyl-3-pyrazolidone etc. Combinations of such developers known to the art and with special adjuvants such as ascorbic acid may be used. The normal additions to developers can be used in all the known combination-s e.g., alkalies such as lithium, sodium and potassium hydroxides, carbonates, alkylamines, :and alkanolamines; borax; sodium metaborate; sodium sulfite; alkali halides e.g., bromide, chloride etc.; surface active agents e.g., polyalkyleneoxide; condensation products e.g., polyglycols, and their ethers and esters; antifoggants e.g., benz'otriazole, 6-nitrobenzimidazole; hardeners e.'g., formaldehyde, alum, glyoxal, glutaraldehyde; image color modifiers e.g., mercaptotetrazoles; alcohols; sequestering agents e.g., the trisodium salt of ethylene diamine tetracetic acid.

Buffers suitable for the process of this invention are those meeting the buffering capacity requirements pre viously specified for one liter of the buffering solution. Namely, that the addition of a 0.1 of an equivalent of sodium hydroxide to the butter solution at a pH of 7.2 causes a rise in pH not less than 0.5 pH unit nor greater than pH units. Buffers having such a buffering capacity are the Potassium dihydrogen phosphate/sodium hydroxide bufier system which has a buffering capacity corresponding to a change of 5 pH units and has the following composition:

(a) Potassium d'ihydrogen phosphate6.80 g. dissolved in 900 mls. of water.

(b) Sodium hydroxide added to bring the pH to 7.20 :.20.

(0) Water added to make 1000 mls. of solution.

Sodium monohydrogen phosphate/citric acid buffer system which has a buffering capacity corresponding to a change of 4.3 pH units and has the =t-ollowing composition:

(a) Sodium monohydrogen phosphate17.9 g. dissolved in 900 mls. of water.

(b) Citric acid added to bring the pH to 7.20:.20.

(c) Water added to make 1000 mls. of solution.

The process of this invention has been found to be highly advantageous in the graphic arts field where it can practically eliminate re-runs of lithographic exposures due to improper development times. The bufier used in the process of this invention stops development promptly and permits development to be re-initiated uniformly thus allowing judgment of development based on time in the developer only without giving rise to density creep. Reinitiation of development using such butters does not involve a second induction period which would lead to unpredictable densities.

The discussion thus far has implied uniform control of development over an entire sheet of film. In addition to this highly useful processing aid, it is also possible to employ the buffer solution in a manner somewhat analogous to that of dodging. For example, if a buffertreated film is under inspection on a safelight table, it may be that only a selected area will be seen to require further development. Such development of localized areas, on either line or halftone exposures, may be readily accomplished by applying to the area in question a cotton swab wetted with developer. Redevelopment will be initiated immediately, and may be terminated when desired by applying another cotton swab wetted with the buffer solution. This aspect of the development control technique offers many possibilities to processing operators. Still additional advantages will be apparent to those skilled in the art of photographic development.

We claim:

1. A process for controlling the development of a photographic film Which comprises:

(1) placing an exposed photographic film containing latent silver halide images which has been partially developed, in an aqueous solution containing at least one buffering compound, said butter solution (a) having a pH below that at which the developer becomes inactive,

(b) having a bufiering capacity such that the introduction of 0.10 equivalent of sodium hydroxide into 1000 milliliters of the unused butter solution at a pH of 72:02 will cause a pH rise of not more than 5.0 pH units or less than 0.5 pH unit, and

(2) reinserting the film in the developer to continue development of the film.

2. A process according to claim 1 wherein steps (1) and (2) are repeated until the desired density is attained.

3. A process according to claim 1 wherein steps 1) and (2) are repeated until the desired silver density is attained and (3) the developed film is then fixed.

4. A process according to claim 1 wherein the buiter solution contains potassium dihydrogen phosphate and caustic soda.

5. A process according to claim 1 wherein the buffer solution contains sodium monohydrogen phosphate and citric acid.

6. A process according to claim 1 wherein the bufier solution contains boric acid and sodium hydroxide.

7. A process according to claim 1 wherein hydroquinone is used as the sole developing agent.

8. A process according to claim 1 wherein the developer is a metol-hydroquinone developer.

References Cited by the Examiner UNITED STATES PATENTS 4/1942 Schilling et al. 96-62 X 2/1951 Friedman 96-63 X OTHER REFERENCES References Cited by the Applicant UNITED STATES PATENTS 2,184,053 12/ 1939 Muehler. 2,239,284 4/ 1941 Draisbach. 2,343,696 3/ 1944 Muehler et a1. 2,541,470 2/1951 Henn et al.

NORMAN G. TORCHIN, Primary Examiner.

C. E. Davis, Assistant Examiner. 

1. A PROCESS FOR CONTROLLING THE DEVELOPMENT OF A PHOTOGRAPHIC FILM WHICH COMPRISES: (1) PLACING AN EXPOSED PHOTOGRAPHIC FILM CONTAINING LATENT SILVER HALIDE IMAGES WHICH HAS BEEN PARTIALLY DEVELOPED, IN AN AQUEOUS SOLUTION CONTAINING AT LEAST ONE BUFFERING COMPOUND, SAID BUFFER SOLUTION (A) HAVING A PH BELOW THAT AT WHICH THE DEVELOPER BECOMES INACTIVE, (B) HAVING A BUFFERING CAPACITY SUCH THAT THE INTRODUCTION OF 0.10 EQUIVALENT OF SODIUM HYDROXIDE INTO 1000 MILLILITERS OF THE UNUSED BUFFER SOLUTION AT A PH OF 7.2$0.2 WILL CAUSE A PH RISE OF NOT MORE THAN 5.0 PH UNITS OR LESS THAN 0.5 PH UNIT, AND (2) REINSERTING THE FILM IN THE DEVELOPER TO CONTINUE DEVELOPMENT OF THE FILM. 